The present invention relates to a process for recovering uranium and/or thorium from a liquid containing uranium and/or thorium which can recover in high yield high purity uranium and/or thorium reutilizable for manufacture of nuclear fuel material.
As a process for recovering uranium and/or thorium contained in liquid wastes discharged from nuclear fuel material handling facilities of nuclear fuel manufacturing factories, the applicant has disclosed water glass precipitation processes in Japanese Patent Publication No. 38,320 of 1973 and Japanese Patent Laid Open Application No. 27,800 of 1978.
In these water glass precipitation processes, the added water glass (sodium silicate) becomes amorphous silica, a powerful adsorbent having a large surface area and a high activity in the solution in which fluorine and ammonia, or nitric acid radical and ammonia, or chlorine and ammonia coexist, forming a precipitate composed mainly of the amorphous silica and having an excellent filterability (hereinafter referred to as an amorphous silica precipitate). At that time, the thus formed amorphous silica precipitate captures by adsorption the uranium and/or thorium contained in the solution, thereby making the uranium and/or thorium removed therefrom. Further, as the uranium and/or thorium captured by the amorphous silica precipitate can be eluted by acid treatment, the uranium and/or thorium can be recovered as an acidic solution by filtering out the amorphous silica precipitate. However, reutilizing the thus recovered uranium and/or thorium directly as nuclear fuel material is difficult because of existence or impurities entered thereinto in the treatment process. Namely, industrial water glass sometimes contains considerable amounts of impurities as Al, Ca, Fe, Mg and the like. In the acid treatment of the amorphous silica precipitate, these impurities are not only eluted together with the uranium and/or thorium to pass into the acidic solution, but also Si, a main component of the precipitate, is partly eluted into the acidic solution. Therefore, in order to reutilize the thus eluted uranium and/or thorium for manufacture of nuclear fuel material, these impurities must be removed to a level which satisfies specifications for impurity required for a nuclear fuel.
As a process for removing impurities of nuclear fuel material, a solvent extraction process or an ion exchange process is adopted widely. These processes, however, decrease the impurity removing ability when Si exists in the nuclear fuel material. Therefore, it is desirable to depress an amount of Si existing in the nuclear fuel material as low as possible.
On the other hand, recently from the viewpoints of enlargement of the treating capacity, improvement of the total yield and decrease of scrap and wastes in nuclear fuel manufacturing factories, reutilization of the nuclear fuel material recovered by the above-mentioned water glass precipitation processes has been strongly demanded.
The present invention is an improved invention of the above-mentioned water glass precipitation processes devised to meet this demand.